Influence of Salmonella specific bacteriophages (O1; S16) on the shedding of naturally occurring Salmonella and an orally applied Salmonella Eastbourne strain in bearded dragons (Pogona vitticeps)

Salmonella in reptiles: a review of occurrence, interactions, shedding and risk factors for human infections

Salmonella are considered a part of the normal reptile gut microbiota, but have also been associated with disease in reptiles. Reptile-associated salmonellosis (RAS) can pose a serious health threat to humans, especially children, and an estimated 6% of human sporadic salmonellosis cases have been attributed to direct or indirect contact with reptiles, although the exact number is not known. Two literature searches were conducted for this review. The first evaluated reports of the prevalence of Salmonella in the intestinal tracts of healthy reptiles. Salmonella were most commonly detected in snakes (56.0% overall), followed by lizards (36.9%) and tortoises (34.2%), with lower detection rates reported for turtles (18.6%) and crocodilians (9%). Reptiles in captivity were significantly more likely to shed Salmonella than those sampled in the wild. The majority of Salmonella strains described in reptiles belonged to subspecies I (70.3%), followed by subspecies IIIb (29.7%) and subspecies II (19.6%). The second literature search focused on reports of RAS, revealing that the highest number of cases was associated with contact with turtles (35.3%), followed by lizards (27.1%) and snakes (20.0%). Reptiles associated with RAS therefore did not directly reflect prevalence of Salmonella reported in healthy representatives of a given reptile group. Clinical symptoms associated with RAS predominantly involved the gastrointestinal tract, but also included fever, central nervous symptoms, problems with circulation, respiratory symptoms and others. Disease caused by Salmonella in reptiles appears to be dependent on additional factors, including stress, inadequate husbandry and hygiene, and other infectious agents. While it has been suggested that reptile serovars may cause more severe disease than human-derived strains, and some data is available on invasiveness of individual strains in cell culture, limited information is available on potential mechanisms influencing invasiveness and immune evasion in reptiles and in RAS. Strategies to mitigate the spread of Salmonella through reptiles and to reduce RAS focus mostly on education and hygiene, and have often been met with some success, but additional efforts are needed. Many aspects regarding Salmonella in reptiles remain poorly understood, including the mechanisms by which Salmonella persist in reptile hosts without causing disease.

Escherichia coli trxAgene as a molecular marker for genome engineering of felixounoviruses

BACKGROUND

Bacterial viruses (bacteriophages or phages) have a lot of uncharacterized genes, which hinders the progress of their applied research. Functional characterization of these genes is often hampered by a lack of suitable methods for engineering of phage genomes.

METHODS

Phages vB_EcoM_Alf5 (Alf5) and VB_EcoM_VpaE1 (VpaE1) were used as the model phages of Felixounovirus genus. The phage-coded properties were predicted by bioinformatics analysis. The 'pull-down' assay was used for detection of protein-protein interactions. Primer extension analysis was used for the DNA polymerase (DNAP) activity testing. Bacteriophage lambda Redγβα-assisted homologous recombination was used for construction of phage mutants.

RESULTS

Bioinformatics analysis showed that felixounoviruses encode DNA polymerase, which is homologous to the T7 DNAP. We found that the Escherichia coli thioredoxin A (TrxA) in vitro interacts with the predicted DNAP of Alf5 phage (gp096) and enhances its activity. Phages Alf5 and VpaE1 do not grow on E. coli strains lacking trxA gene unless it is provided in trans. This feature was used for construction of the deletion/insertion mutants of non-essential genes of felixounoviruses.

CONCLUSION

DNA replication of phages from Felixonuvirus genus depends on the host trxA, which therefore may be used as a molecular marker for their genome engineering.

GENERAL SIGNIFICANCE

We present a proof-of-principle of a strategy for targeted engineering of bacteriophages of Felixounovirus genus. The method developed here will facilitate the basic and applied research of this unexplored phage group. Furthermore, detected functional interactions between the phage and host proteins will be significant for basic research of DNA replication.

Influence of Salmonella specific bacteriophages (O1; S16) on the shedding of naturally occurring Salmonella and an orally applied Salmonella Eastbourne strain in bearded dragons (Pogona vitticeps)

This study determined the passage time and phage propagation time of salmonella specific phages, Felix O1 and S16, in 10 bearded dragons, based on re‐isolation from cloacal swabs and faecal samples following oral administration, as a possible tool for reducing salmonella shedding. In Study 1, Felix O1 was administered orally for 12 consecutive days. Over 60 days, swabs were taken from the oral cavity and cloaca and qualitative Salmonella detection as well as salmonella quantification from faecal samples were performed. In Study 2, a phage cocktail (Felix O1 and S16) was administered to half of the tested animals. Salmonella (S.) Eastbourne was also given orally to all animals. Oral and cloacal swabs were tested as in Study 1, and faecal samples were collected for phage quantification. Various Salmonella serovars were detectable at the beginning of the study. The numbers of serovars detected declined over the course of the study. S. Kisarawe was most commonly detected. Salmonella titres ranged from 10² to 10⁷ cfu/g faeces. The phages (Felix O1 and S16) were detectable for up to 20 days after the last administration. The initial phage titres ranged from 10³ to 10⁷ pfu/ml. The study shows that the phages were able to replicate in the intestine, and were shed for a prolonged period and therefore could contribute to a reduction of Salmonella shedding.